The invention relates to an arrangement for monitoring and fault diagnosis in the communication controller of a line termination unit in program controlled data switching systems of modular construction, with individual devices for the detection of faults and for the emission of fault signals, in which safeguarding programs take place for purposes of fault diagnosis.
In a program controlled data switching system, the incoming and outgoing lines are connected to a processing unit. This processing unit, which is referred to as line termination unit in the following, enables cyclic traffic with the central units of the system. The fundamental component of the central unit is the central storage unit which contains all the items of information required for the execution of switching functions and for the execution of safeguarding processes.
The line termination unit, which serves as link between the incoming and outgoing lines and the central components of the exchange, contains connection circuits which are assigned to the lines, input and output code converters which identify the connection circuits, and at least one communication controller which handles the data traffic between the line termination unit and the central parts of the exchange.
The construction of a line termination unit is described in detail in U.S. Pat. No. 3,717,723 in respect of the connection circuits and the input-output code converters. Therefore, only the essential features of the mode of operation will be described hereinbelow.
If an item of information, e.g., in the form of a polarity change, arrives on one of the connected lines, a cycle request is produced in the connection circuit assigned to this line. At the same time, the connection circuit which is offering the request is identified with the aid of the input code converter. The transfer of the cycle request to the central storage unit is carried out in the communication controller. With the aid of the address of the connection circuit which has been determined in the input code converter and has been coded accordingly, a specific feeder cell in the central storage unit which is permanently assigned to this connection circuit is accessed. This cell contains all the further items of information required to handle the item of information which has arrived. For example, as a result of the read out of the feeder cell, the address of a specific connection circuit is produced with which this connection circuit is identified by the output code converter. The line connected to this connection circuit is then given the information, in the present example, the new polarity change.
If, however, this is a connection which has not yet been switched through, on the arrival of an item of information on an incoming terminal, a series of programs are started which lead to the incoming item of information being evaluated as a call criterion and the appropriate switching reactions taking place. This is carried out under the control of specific programs, the execution of which leads to the prompt production and transmission of items of information and to the prompt evaluation of received items of information.
From U.S. Pat. No. 3,768,079 it is known to write into the feeder cells, in program controlled fashion, criteria which are read out by the communication controller of the line termination unit during a cycle relating to the feeder cell, and are evaluated for the handling of the arrived information. In this way it can be very rapidly established whether the incoming item of information is to be passed on to an outgoing connection circuit or whether it is to be entered in specific storage zones of the central storage unit. Such a storage zone is for example the so-called note pad store which is processed in specific time intervals by a program control unit.
From this patent it is also known to enter commands into another storage zone of the central storage unit under the control of the program control unit. This storage zone, the so-called command block store, is processed at specific intervals of time by the communication controller. The commands which are thereby read out can in turn be entered, together with an indication of the time of their execution, as so-called prompting commands in the notepad store. This in itself achieves a significant improvement in respect of the extreme real time requirements.
In this connection, commonly assigned U.S. application Ser. No. 552,796, filed Feb. 25, 1975, and now abandoned, which is a continuation of U.S. application Ser. No. 470,086, filed May 15, 1974, which is a continuation of U.S. application Ser. No. 265,654, filed June 23, 1972 discloses a further measure which consists in that at least those items of information which are offered for addressing purposes to the central storage unit, are intermediately stored in the communication controller. To this end one uses a so-called cycle buffer store. After the output of the information contained in the addressed storage zone, this information is checked in an evaluator circuit. In dependence upon the evaluation of the output stored data, it is established whether the cycle which has just been carried out is to be followed by further cycles, i.e., whether any further treatment is necessary or not. If it is established that the item of information, on the basis of which this first cycle has been carried out, need only be passed on to a specific connection circuit, no further cycles are required. If, however, it is established that a further cycle is in fact needed, the essential data required for this purpose are available in the cycle buffer store. In this case the intermediately stored data are transferred into a second buffer of the communication controller, the so-called subsidiary cycle buffer store, from which they are available for any additional cycle, if required. For this purpose, the subsidiary cycle buffer store (emits a cycle request in the known manner. The items of data contained in the subsidiary cycle buffer store are offered by the output registers of the communication controller to the store, and again to the cycle buffer store. This process can then be repeated if the read out stored data again require a subsequent processing of this information.
A most essential requirement for a program controlled data exchange is that of constant availability. By employing a generally known principle, the availability is increased by means of a modular construction. A further measure to improve the availability consists in introducing determinate function states for the individual units of the system. A proposal to set the individual system components into an operating state, a test state and a breakdown state, is described in U.S. Pat. No. 3,818,199. For this purpose the individual system components contain devices, for example, comparator devices of fault recognition circuits. The introduction of these states permits, by suitable safeguarding programs, the localization and diagnosis of faulty units, with the cooperation of fault-free parts of the system without these fault-free parts being affected by the faulty unit.
When applied to the line termination unit, these principles mean that the communication controller is provided at least twice, and that both communication controllers operate in parallel and in synchronism. Thus, it is possible to detect a faulty operation by means of comparator circuits, so that it is possible, when one communication controller is operating defectively, to maintain the operation without limitation by the other correctly functioning communication controller.
In FIG. 1 a system is illustrated in which the line termination unit LE contains two communication controllers UEAS1 and UEAS2 which are of identical construction, operate in parallel and cooperate with two storage units SE1 and SE2 which are likewise of identical construction.
Each of the two communication controllers UEAS1 and UEAS2 contains data input and data output devices DE and DA to which are connected the input and output code converters ECW and ACW. In the direction to the storage units SE1 and SE2 are arranged the registers SSAR, AdAR and WAR. By the register SSAR, the items of data required for the operation of the storage units, such as data concerning the store selection, concerning the store operations code, concerning the store operation mode etc are output. By the register AdAR is output the store address and via the register WAR is output the store word. The word input register WER is provided for the transfer of the read-out store word. In addition to the information lines, there are also provided a number of control lines of which only the lines serving to transmit the signals PSS, PVS and FVS are entered. Details in this respect will be explained hereinbelow.
Comparator circuits VG provided in the storage units SE1 and SE2 and in the input and output code converters ECW and ACW monitor the synchronous operation of the communication controllers UEAS1 and UEAS2. The communication controllers UEAS1 and UEAS2 also contain fault detection circuits which emit a fault signal FA in the event of a fault.
On the detection of a fault in known manner, safeguarding programs, i.e., localization and diagnosis programs, are activated which locate the fault and establish the faulty unit or circuit. At this point, the relevant communication controller can assume the described test state.
The invention is concerned with the problem of increasing the availability of the line termination unit in a program controlled data switching system of this kind. For this purpose it is based on the following conditions:
1. Faults which fundamentally affect the operation of the communication controller are recognized by individual fault detection circuits.
2. A faulty communication controller can be blocked in relation to the fault-free units of the system through the introduction of a determinate test state.
3. The diagnosis of a faulty communication controller or of parts within a communication controller is carried out in conjunction with safeguarding programs; the sequences which are controlled by this means rapidly and accurately locate faults.
An object of the invention is to provide means which will improve the capability for diagnosis faults in systems like that described herein by means of additional circuits in the communication controllers.
In this context, a further object of the invention is to provide means in the communication controller itself by which an accurate description can be formed of any fault which is occurring.
An additional object is to provide an arrangement which includes in the diagnosis all attainable data and information required for the operation of the communication controller, and if possible also for cycles which have already been carried out.
Still another object is to provide means for fault recognition in which the fundamental sequences in the communication controller can be started in program controlled fashion and the result be traced.